1. Field of the Invention
This invention relates to microbicidal compositions that are particularly suited to controlling the growth of microorganisms in aqueous systems. More particularly, compositions comprising combinations of a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one with 2-hydroxypropyl methanethiolsulfonate are useful in controlling the growth and proliferation of slime-forming bacteria, fungi, and algae in commercial and industrial cooling water systems, cooling towers, evaporative condensers, air-washing systems, and industrial water supply and process water systems.
2. Description of the Prior Art
The formation of slime caused by the growth and multiplication of slime-forming microorganisms if not controlled is a serious problem. For example, lagoons, lakes, ponds, pools, and such systems as cooling water systems and pulp and paper mill systems all possess conditions which are conducive to the growth and reproduction of slime-forming microorganisms. In both once-through and recirculating cooling systems, for example, which employ large quantities of water as a cooling medium, the formation of slime by microorganisms is an extensive and constant problem.
Airborne organisms are readily entrained in the water from cooling towers and find this warm medium an ideal environment for growth and multiplication. Aerobic and heliotropic organisms flourish on the tower proper while other organisms colonize and grow in such areas as the tower sump and the piping and passages of the cooling system. Such slime serves to deteriorate the tower structure in the case of wooden towers. In addition, the deposition of slime on metal surfaces promotes corrosion. Furthermore, slime carried through the cooling system plugs and fouls lines, valves, strainers, etc. and deposits on heat exchange surfaces. In the latter case, the impedance of heat transfer can greatly reduce the efficiency of the cooling system.
In pulp and paper mill systems, slime formed by microorganisms is also frequently and, in fact, commonly encountered. Fouling or plugging by slime also occurs in the case of pulp and paper mill systems. Of greater significance, the slime becomes entrained in the paper produced to cause breaks on the paper machines with consequent work stoppages and the loss of production time or unsightly blemishes in the final product which result in rejects and wasted output. Likewise, lagoons, ponds, lakes and even pools, either used for pleasure purposes or used for industrial purposes for the disposal and storage of industrial wastes, become, during warm weather, excellent habitats for the growth reproduction of slime-forming microorganisms. In the case of the recreation areas, the problems of infection, etc., are obvious. In the case of industrial storage or disposal of industrial materials, the microorganisms cause additional problems which must be eliminated prior to either the materials' use or the disposal of the same in any type of waste disposal unit.
The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and pulp and paper mill systems. Materials which have enjoyed wide-spread use in such applications include chlorine, organo-mercurials, chlorinated phenols, organo-bromines, and various organo-sulfur compounds. All of these compounds are generally useful for these purposes, but each is attended by a variety of impediments. For example, chlorine must be used at a high concentration for the effective control of organisms. This is probably true in part at least because chlorine is very reactive chemically thus reacting with various components present in the system before its full biocidal function can be achieved thus increasing cost. Other biocides are attended by odor problems and hazards in respect to storage, use or handling which limit their utility. To date, no one compound or type of compound has achieved a clearly established predominance in respect to the applications discussed.
Naturally, economy is a major consideration in respect to all of these biocides. Such economic considerations attach to both the cost of the biocide and the expense of its application. The cost performance index of any biocide is derived from the basic cost of the material, its effectiveness per unit of weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated. To date, none of the commercially available biocides have exhibited a prolonged biocidal effect. Instead, their effectiveness is rapidly reduced as the result of exposure to physical conditions such as temperature, association with ingredients contained in the system toward which they exhibit an affinity or substantivity, etc., with a resultant restriction or elimination of their biocidal effectiveness.
As a consequence, the use of such biocides involves their continuous or frequent addition to systems to be treated and their addition to a plurality of points or zones in the systems to be treated. Accordingly, the cost of the biocide and the labor cost of such means of applying it are considerable. In other instances, the difficulty of access to the zone in which slime formation is experienced precludes the effective use of a biocide. For example, in a particular system there may be no access to an area at which slime formation occurs and the biocide may only be applied at a point which is upstream in the flow system. However, the physical or chemical conditions, e.g., chemical reactivity, thermal degradation, etc., which exist between the point at which the biocide may be added to the system and the point at which its biocidal effect is desired, may render the effective use of a biocide impossible.
Similarly, in a system experiencing relatively slow flow, such as a paper mill, if a biocide is added at the beginning of the system, its biocidal effect may be completely dissipated before it has reached all of the points at which this effect is desired or required. As a consequence, the biocide must be added at a plurality of points, and even then a graduated biocidal effect will be experienced between one point of addition to the system and the next point downstream at which the biocides may be added. In addition to the increased cost of utilizing and maintaining plural feed points, gross ineconomies in respect to the cost of the biocide are experienced. Specifically, at each point of addition, an excess of the biocide is added to the system in order to compensate for that portion of the biocide which will be expended in reacting with other constituents present in the system or experience physical changes which impair its biocidal activity.
It is disclosed in U.S. Pat. No. 3,859,322 that hydroxyalkyl esters of thiosulfonic acids are useful for the control of slime-forming microorganisms in industrial processes involving water. One such ester, 2-hydroxypropyl methanethiosulfonate, is now an article of commerce, being sold by Buckman Laboratories, Inc., under the tradename HPMTS.
It is disclosed in U.S. Pat. No. 3,929,561 that the mixture of 75% of 5-chloro-2-methyl-4-isothiazolin-3-one and 25% of 2-methyl-4-isothiazolin-3-one which is sold under the trademark Kathon.RTM. 886 by Rohm and Haas may be blended with certain sulfones to produce a synergistic biocide. In U.S. Pat. No. 4,295,932, it is disclosed that combining the use of Kathon.RTM. 886 along with treatment of an aqueous system with chlorine dioxide provides synergistic microbicidal action. In U.S. Pat. No. 4,379,137, it is disclosed that an admixture of a polymeric quaternary ammonium compound and compounds of the type of which Kathon.RTM. 886 is composed is a synergistic disinfecting and preserving composition that is useful for protecting aqueous systems against contamination by deleterious microorganisms. Kathon.RTM. 886 and these synergistic blends are claimed to be effective at low dosages, e.g., a few parts per million, for treating industrial water systems to control the growth of bacteria, fungi, and algae.
It is a principal object of our invention to provide a composition which obviates the disadvantages of the prior art biocidal compositions. Other objects and advantages of our invention will become apparent as the description proceeds.